This invention relates generally to coupling of light into optical fibers and more particularly the coupling of pump light from a multi-wavelength pump source or sources into one or more double clad fibers, which fiber or fibers may include an active element in the core.
Doped double clad fibers have come into use providing for higher output power from fiber amplifiers and fiber lasers than can be achieved from employing a doped single mode fiber. With the larger inner pump cladding of the double clad fiber, high power multimode laser diodes can be employed to provide for coupling large amounts of pump power into the inner cladding, allowing the scaling of fiber amplifier powers to much higher levels than those available from a conventional single mode fiber amplifier. The multimode nature of these multi-wavelength sources, however, precludes the use of fused WDM couplers for combining the pump and signal into the fiber amplifier. In cases of employing such multi-mode sources, an optical lens system may be employed to couple the multimode light into an input fiber having a high numerical aperture (NA). However, higher optical losses are a result of such free-space optical coupling systems.
An all-fiber fused approach for coupling the multimode pump light into the fiber would be preferred over such free space optical coupling architecture because it provides for a more robust arrangement, comparatively easier alignment and is less expensive to manufacture. It would also be preferable to pump the fiber gain media with a number of discrete fiber coupled lasers in a distributed pump architecture where the respective pump lasers may be individually addressed. Such a pumping arrangement has advantages in providing for thermal distribution and increased lifetime of the discrete laser diodes as compared to employing a single laser bar as a pump source. Also, an all-fiber fused approach would permit the use of a low cost utility amplifier system for amplifying a plurality of communication signals via a plurality of fused coupled fiber amplifiers with a single high multimode laser pump source.
According to this invention, all-fiber coupling architectures include at least one fiber gain media, e.g. a fiber amplifier or a fiber laser, providing for the coupling light from one or more multi-wavelength pump sources propagating in a multimode core fiber at multiple points along a double clad fiber or at least at one point along multiple double clad fibers having their inner claddings fused to the multimode core fiber. The latter arrangement provides for a low cost utility multi-signal fiber amplifier for telecommunication applications.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.